Resonating chamber construction for pianos



Sept. 27, 1949.

Filed June 4, 1947 H. o. CRIPPEN, SR 2,483,087

RESONATING CHAMBER CONSTRUCTION FOR PIANOS 2 Sheets-Sheet 1 Sept. 27, 1949. H. o. CRIPPEN, SR

RESONATING CHAMBER CONSTRUCTION FQR PIANOS 2 Sheets-Sheet 2 Filed June 4; 1947 N MN fnvenior: flerberz'f 0' (rip 0.92 5).

Patented Sept. 27, 1949 :SIATES s-RESONATINGJICHAMBER; CONSTRUCTION FOR PIA-NOS Herbert 0; Crippen, S12, Chicago, 111.

:-;Application June 4, 1947, Serial No. 752,489

4' Claims. ,1

This invention relates totan imrn ovementv in pianos, andmoref-particularly to an improvement Wheri eby the tonal qualities. or characteristics of pianos, either of the'grandor uprights types, may beisignificantly improved. .Thisi-mprovement is obtained by equipping the pianqsswith an effective resonating chamber. "If-hissapplicationv is a continuation in; part; :of'. my; co-pending application, Serial'No,.- 526,262, filed,March13,--194i now forfeited.

Inconventional constructions of pianos, which have longsbeen moreor less the same-byaall manufacturers, a sounding board is suitably-supported around its edges by mountingon the side frame or rim of'the piano-case,thestrings of the instrument ;being stretchedbetween points one metal frame and a pin blockas usual and disposed adjacent one face. of thesounding board, the other face ofv the sounding board being provided with reinforcing ribs andleftexposedto-the atmosphere. ,In other words, the, bottom of a grand piano and the backoffanzupright orsspinet vtype piano :have-beem left; open o XPDse-the bottom or back of thes-oundingboard visibly to the atmosphere outside of the piano case.

I have previously proposedthe application of a resonatingcharnber to a piano sounding board by attachment, of a specially constructed chamber to the central, portion or 'bacleof the sounding board accompanied bythe removal of the reinforcing rib portions in the area covered by the special resonating chamber. This is shown in my Patent 1,530,984 issued -March .24, 925. That construction has been considered-impractical for various reasons-such astherequired changing of the accepted piano structure including the removal of the "sound board reinforcing ribs or portions thereof and the resulting loss ofsounding board reiniorcement and impairment-of its musical functions, interference with proper vibration ofithe sounding board by the attachmentlof the resonating chamber tothebottom or back of the sounding boardythe high cost of'constructing the special chamber, the great difficulty 01 securing-effective attachment thereof to the sounding board without the tabooed use of nails or screws entering the sounding board, the impracticality of placing the-to1iepost between the sounding board: and the back of the chamber under adequate compression between said sounding board and back because-ortheinherent weakness of attachmentof the. resonating chamber to the sounding board, and'perhaps other reasons.

The main object ofthepresent'inventi-on is to provide an effectiveir'resonating chamber in a piano without requiring significant changesin the construction of the sounding boardits reinforcement, the. piano frame orcase orany other part of the conventional pianostructure. Another object is -to provide a piano resonating chamber which can be produced and applied at a veryslow cost so as toavoid unduly increasing the cost of constructing a? piano embodying the improved resonating chamber. Still another ob 'ectis, as already indicated, to provide apiano resonating chamber which will accomplish its resonating function without. incidentally impair? ing the normal functioning of the sounding board, and, in general, it is the objectof the invention to provide a piano embodying. improved tonal .quanities or characteristics without materially complicating orlincreasing the cost of constructing theinstrument.

iOther objects and advantages of the invention will .be.understoodby reference to the following specification "and accompanying drawings wherein the applicationof a resonating chamber according to the present invention is illustrated in respect of both a grand and an upright piano In-the drawings Fig. ltis a top, plan of a grand pian0 ,the cover being omitted;

Fig. 2 is a bottom plan of the grand piano, a part being shown broken away to more clearly illustrate certain details;

lEig. -3=.is a fragmentary,perspective illustrating the principal detailsof construction with which this application is concerned; and

Figs. 4 and 5 are backand transverse sectional views respectivelyof an uprightpiano to, which the invention is applied.

In a so-called grand piano, that is a piano in whichthe sounding board and'str-ings are disposed in a substantially horizontal plane, the presentimprovement is embodied by mounting a rather stiiT or rigid wood panel I in the piano case or frame so as to close the bottom area thereof, and by interconnecting such panel and thesounding boardlZ of the piano by means of one or more tone postssuch as shown at 3. Also,

thelsoundingboardis equipped with one or more sound openings or holes '4.

The piano case consists of a frame or rim members5 which: extendstaround the backland across the sides of the piano, usually terminating-at a junction-with the key. section. 'Within the member 5. there isa reinforcing rim or element 6, usually somewhat thickerthan the wood of which the member 5 is, formed. The sounding board Z is mountedwaround itsrrear and side portions, on

the upper edge 1 of said reinforcing member 5, the sounding board usually being securely glued to said edge I.

The strings indicated at 8 are stretched in the customary manner between pins carried by a pin block (not shown) and pins carried by a metal frame or string plate 9 which is disposed above the soundin board 2 in spaced relation thereto except to the extent that the plate 9 may have boss-like marginal portions seated directly on the sounding board or on a suitable mounting strip or block in accordance with conventional practice. The string plate is, of course, suitably secured to the underlying portions of the case reinforcement 6. The usual curving bridge [0 is interposed between the strings and the sounding board in the usual manner.

The front edge of the sounding board, that is the edge thereof which extends substantially parallel to the length of the keyboard of the instrument, is supported on the upper edge of a transverse frame member II which extends between and joins the opposite end portions of the outer case 5 and its inside reinforcing member 6.

On the bottom side of the sounding board, there are provided a series of diagonally extending stiffening ribs [2, these ribs being applied to the sounding board in a conventional manner and serving their usual purposes of reinforcing the sounding board and transmitting or spreading vibration over the area of the sounding board transversely of the grain direction of the sounding board. The sounding board and reinforcing ribs are of straight grained spruce-pine construction as usual.

The sounding board 2 is set in motion in harmony with the vibration imparted to the strings 8, mainly by motion transmitted from the strings to the sound board through the bridge 10, and the vibratory motion of the sounding board is transmitted through the agencyof said one or more tone posts to the back panel of the resonating chamber formed by the panel I.

The illustrated tone post 3 is shown located at a point of the sounding board substantially in register with a portion of the bridge, approximately under or adjacent to the point at which the middle C strings cross over the bridge. A single sound opening may be provided in the sounding board 2 adjacent said tone post 3 and preferably forwardly of the bridge. Additional tone posts and openings, or either of them, may be provided, For example, as shown in Figs. 1 and 2, a sound opening is provided in association with the opening 4 but beyond or to the rear of the bridge, said openings 4 and 4a constituting one pair of openings with the tone post 3 between them, and similar pairs 4b and 4c of openings are provided at suitable points above and below the middle C location of the tone post 3 and opening pairs 4 and Ad. In this instance, there is no tone post (other than the middle C tone post) associated with the opening pairs 4?; and 4c.

Larger pianos may advantageously be provided with two or more sound openings or two or more pairs thereof, whereas smaller pianos may be adequately served by a single opening. Also, the size and shape of the opening as well as the number and location thereof may be varied to procure the desired tonal effects.

Sounding boards are usually crowned or arched somewhat, often so that a central point is ap proximately inch higher than its periphery. The reinforcing ribs l2, of course, are made to conform to such arching, the sounding board being usually of substantially uniform thickness so that on the bottom side, the sounding board is concave in parallelism to the convex arching of the top or string side. This arched construction serves to aid the sounding board to withstand the pressure exerted thereon by the strings which are under very high tension so that they exert considerable down pressure (often of the order of 600 pounds) on the bridge and on the sounding board. This down pressure is a steady load subject to relatively small changes resulting from the vibration of the strings. Hence, it can be seen that the sounding board must be a very strong unit, and for lasting results, must be adequately braced by ribs such as the ribs l2 to prevent its being collapsed by the said down pressure of the strings.

The tone post 3 is preferably fixedly positioned by having its lower end recessed into the closure panel as shown at l3, the fit being a drive fit so that there can be no significant relative movement between the tone post and the closure panel I. The sounding board end of the tone post is caused to tightly abut the bottom of the sounding board, but it is preferably not recessed into the latter because of the difficulty of properly aligning recesses therein with the closure panel recesses to receive the opposite ends of the tone posts, and because of other reasons, including the weakening effect of recesses if out into the sounding board.

The tone post is preferably made of the same material as the sounding board and its reinforcing ribs, and it is selected of such length that when the instrument is assembled, the tone post will be under sufficient compression between the sounding board and the closure panel to prevent the occurrence of any significant relative movement between the sounding board and the adjacent end of the tone post, or between the closure panel and the adjacent end of the tone post whether or not any adhesive is applied at the ends of the tone post. Normally, the recessed seating of the tone post will be suificient to position it without any other fastening.

In constructing a piano, the case structure will be produced in the usual manner, but before the sounding board is inserted, the closure panel I may be seated on an inwardly projecting ledge provided by an inwardly projecting shoulder strip or closure mounting strip [4 which is preliminarily secured by gluing (with or without additional fastening) to the lower portion of the reinforcing rim element 6. The closure panel will preferably be adhesively secured to said mounting strip l4 adjacent the side portions of the piano, and at its front end, said closure panel will be similarly supported on a mounting strip l5 which is secured to a transverse frame member is which is a standard part of a conventional grand piano construction. Said transverse member H5 is secured to a bottom member H of the keyboard section of the piano.

Either before or after the closure panel I is properly secured in place, the tone post 3 (or all that are used) are seated in the closure panel as already explained. Thereafter, the sounding board is set into the case and secured on the supporting inner frame 6 in the usual manner followed by application of the string plate, strings, etc. The sounding board is securely held down by its own attachment to the frame part 6 and additionally by the attachment of the overlying string plate to said frame part. Hence, the sounding board and closure panel are each secured to said case part 6 so as to be well a a ted: tor-ma ntain saidtene PQ$$ ser e -sebn el Pr su be teemt as e oesiins hamtsp reride ue lll il th s1 er s mekh t name of t e p an One such hammeris represented in the drawass at Ill.

The closure panel I may be made of any suit able wood or other material. piano practices, it is preferable that the closure panel I be constructed of clear hard maple, and preferably in the form of strips joined edge to edge by gluing substantially in accordance with the construction of a conventional sounding board; the strips may have tongue and groove connections if desired.

Grand pianos are usually made with one or more transverse braces such as represented by dotted lines it. Wardly from the sounding board so as to avoid any interference with the proper functioning thereof. These transverse reinforcing braces may be entirely dispensed with since their function will be substantially performed by the closure panel which is secured to the side frame or rim of the piano case. The saving in cost incident to the said elimination of these usually heavy braces, and the labor of applying them, will largely, if not wholly, cover the cost of providing and installing the described resonator elements.

In general, the only change involved in embodying the described resonating chamber is to eliminate the heavy frame braces underlying the sounding board, provide a supporting ledge such as the ledge i l-45, and to provide and seat the closure panel i with its tone post (or posts). This departure from standard piano construction thus involves no radical changes in standard constructions, but mainly the provision of the additional elements indicated. Hence, the production of a piano with the improved resonating chamber involves no extensive new details of construction, and involves no modification of established and accepted principles of piano construction. Also, these additional elements are of simple and relatively inexpensive character which should add but little to the cost of the instrument in View or" the saving effected by omitting the heavy frame braces.

A resonating chamber may be provided in an upright type of piano as represented in Figs. 4 and 5, wherein a closure panel 29 is shown recessed into the back of the piano and seated on mounting strips 21 secured to the sides 2"-22 of the piano case and on frame members 2-3-23 which extend across the top and botton of the case at the back thereof. The rib reinforced sounding board 24 is provided with a plurality of pairs of sound openings in the form of r. it f tqn s sse ve-.4 4 SP -1Qll$P @tetwee @t e jop mnss 9 each I so that rancly fl, sup lies allt in o semfin .ct e yq redli w ve i f e erre ssui etsrrmetiee im ose o it the In view of present Such braces are spaced downsnsd-h9lee-suehrserepresented at isl nds? The tone posts are under compression;; l etw gn th s ndin imam: iend-hwkmane 2 s s nt lly. a abo .er ein din cennsclthn w t h a 120st. 3 .ari ;.the--Qi ndie board. an

b khand le conve ona rticall -e tsndiesainte s g eom tted sin th st n be side of the closure-pa e flye h wee t 9. .e :29- and; t e soundin board-12 3,.- dspen l ns; 11120.

construction details of the piano to whicl'nthe Some technicians assert that the point of greatest vibration of the strings and sounding board occurs at a point equal to about /8 of the length of the respective strings forwardly of the bridge. The sound opening or openings and also the tone post or posts may accordingly be located a corresponding distance forwardly of the bridge, 1. e. /8 of the length of the overlying strings forwardly of the bridge. Hence, in Figs. 1 and 2 the sound openings which are located forwardly of the bridge are shown at progressively varied distances from the bridge while the openings to the rear of the bridge are located at approximately uniform distances from the bridge. Similarly, in Fig. 4, the pairs of openings and associated tone posts are shown at different distances from the bridge.

Various changes in the details of the described construction and in the positioning of the tone posts and sound openings, as well as in the number of said tone posts and the shape and number of said openings may be made while employing the principles of the invention.

I claim:

1. A piano having a sound board, tensioned strings on the front side of said sound board, a case or frame extending around said sound board and supporting the same, said frame extending laterally from the sound board beyond the back side thereof so as to cooperate with the sound board to form a recessed area, a closure panel for said recessed area secured directly to said case in spaced relation to said sound board, said closure panel cooperating with said case and sound board to form a resonatin chamber, said resonating chamber being provided with a sound opening communicating with the interior of said chamber.

2. A piano having a case and sounding board mounted on the case Within the same, tensioned strings extending over one face of said sounding board and reinforcing ribs secured to the opposite face of said board, said case extending laterally from said sounding board beyond its rib reinforced face so as to cooperate with said sounding board to provide a recessed area within said case, a closure panel spaced from said sounding board an peripherally mounted on said case independently of said sounding board, and a tone post under compression between said sounding board and closure panel, said sounding board, case, closure panel and said tone post cooperating to form a resonating chamber, said resonating chamber being provided with a sound opening communicating with the interior of said chamber.

3. In a piano, a sound board bowed to provide a substantially convex surface, a plurality of vibratory strings arranged over said surface, a bridge on said surface over which said strings are tensioned, said sound board having a plurality of spaced pairs of f-shaped holes located inwardly of said bridge in areas coinciding with the regions of the greatest vibration of said strings, a wall substantially coextensive with said sound board and spaced therefrom, and a tone post located between each pair of f-shaped holes, said tone posts being under compression between and intimately connecting said sound board and said wall.

4. In a piano, a resonant chamber comprising a sound board bowed to provide a substantially convex surface, a wall substantially co-extensive with said sound board and spaced therefrom, a

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 293,414 Caddick Feb. 12, 1884 1,288,152 OShaughnessy Dec. 17, 1918 1,694,789 Muchey Dec. 11, 1928 

